"Women who douche are almost twice as likely to get ovarian cancer," Metro reports after a study of more than 40,000 women from the US and Puerto Rico found a significant link…

"Women who douche are almost twice as likely to get ovarian cancer," Metro reports after a study of more than 40,000 women from the US and Puerto Rico found a significant link between douching and ovarian cancer – almost twice the risk of no use.

Vaginal hygiene is important – the use of plain unperfumed soaps to wash the surrounding areas is advised, while the vagina cleans itself with natural secretions.

But a douche flushes water up into the vagina and clears out natural secretions designed to keep the vagina healthy, which may increase the risk of infections.

There are concerns some douching products could introduce phthalates – chemicals that may disrupt hormone regulation – into the reproductive tract, which could increase the risk of ovarian cancer.

Concerns have also been raised that genital talc, often used in combination with douching, may increase cancer risk. But as we discussed earlier this year, evidence about this link is inconclusive. This study did not find a significant link for talc use.

Although this appears to be a large study, the number of women with ovarian cancer and a history of douching or talc was small, at just 40 people. This reduces confidence in the results.

Still, why take the risk at all? In a recent interview with NHS Choices, Professor Ronnie Lamont, spokesperson for the Royal College of Obstetricians and Gynaecologists said: "I can't think of any circumstances where douches are helpful."

Where did the story come from?

The study was carried out by researchers from the National Institute of Environmental Health Sciences in the US, who also provided funding for the study.

The study has been reported widely and accurately in the UK media. For example, The Independent explained the study cannot prove causality because a "precise link between the two is unknown, as correlation does not necessarily indicate causation.

"Other factors could be at play, including that women who notice discomfort or infections in their genital area are more likely to douche while also indicating poor ovarian health."

Many sources, such as The Sun, also made the point that women "should NEVER douche".

What kind of research was this?

This prospective cohort study followed women without ovarian cancer over an average of 6.5 years.

It aimed to see if women who developed ovarian cancer over the course of the study were more likely to perform douching or use talc on their vaginas.

This type of study is still only able to find associations and cannot prove cause and effect, but it is the most appropriate study design for investigating whether a behaviour appears to be risky or not.

But the gold standard in study designs – a randomised controlled trial – would be unethical as it would expose participants to a potential risk.

What did the research involve?

This study looked at data from women from the US and Puerto Rico involved in the Sister Study, which, as the name suggests, is an ongoing cohort study involving sisters originally set up to look at breast cancer risk factors.

Women aged 35 to 74 years who were free of breast cancer and had a full or half-sister with breast cancer were enrolled in the study in 2003 and followed up until 2009.

At the start of the study participants completed telephone interviews, which included questions on their reproductive history, health conditions and lifestyle factors.

Women were excluded if they had their ovaries removed or ovarian cancer, or had no follow-up information.

The women also completed a questionnaire on their personal care, including douching and talc use in the previous 12 months. Participants were grouped as "never used" or "ever used" for the analysis.

Follow-up questionnaires were completed every two to three years and collected information on the women's health.

In July 2014 the researchers analysed data to establish the incidence of ovarian cancer. Hazard ratios were calculated controlling for the effects of possible confounders, including menopausal status, duration of oral contraceptive use, and body mass index.

What were the basic results?

A total of 41,654 women were included in the analysis and followed for around 6.6 years. During the follow-up period 154 participants reported a diagnosis of ovarian cancer.

Douching in the 12 months before study entry was reported in 20% of those with a diagnosis of ovarian cancer and 13% of non-cases.

Talc was used in the 12 months before the study start by 12% of women who developed ovarian cancer and 14% of those who did not.

This meant there was no statistically significant association between talc use and ovarian cancer (HR 0.73; CI 0.44 to 1.2).

How did the researchers interpret the results?

The researchers concluded that, "Douching but not talc use was associated with increased risk of ovarian cancer in the Sister Study."

Conclusion

This cohort study investigated the association between ovarian cancer and both douching and talc use.

Using participants in the Sister Study, the researchers found a significant link between douching and ovarian cancer – almost twice the risk of no use. No significant link was seen for talc use.

The results need to be viewed with caution, however, as they are based on small numbers: just 40 women with ovarian cancer who had douched or used talc.

The study has other important limitations, but the main concern is it is not able to prove direct cause and effect. It may be that women with irritation or poor vaginal health would be more likely to use douching methods.

And although the researchers attempted to control for various confounders that may be influencing the link, it is possible these have not been fully accounted for and other health and lifestyle factors were missed.

Crucially, the researchers did not adjust their results to take into account the fact women who developed ovarian cancer were more likely to have a first-degree family history of ovarian cancer and more than one first-degree relative with breast cancer. Nor did they account for smoking, another risk factor for ovarian cancer.

The International Agency for Research of Cancer has classified genital talc as a possible carcinogen. So far there have been mixed results from other studies assessing the link, and further research in the form of good-quality prospective studies would be required to confirm this.

Vaginal hygiene is important to most women. But it is recommended that perfumed soaps, gels and antiseptics are avoided, as they can affect the healthy balance of bacteria and pH levels, and cause irritation.

A douche flushes water up into the vagina, clearing out vaginal secretions – this means using a douche can disrupt the normal vaginal bacteria and may increase risk of infections.

The use of plain, unperfumed soaps to wash the surrounding areas is advised, and the vagina will clean itself with natural secretions.